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Babcock, Horace Welcome


Pasadena, California, 13 September 1912; d. Santa Barbara, California, 29 August 2003)

astrophysics, solar physics, science administration, instrumentation.

Babcock is best known as a pioneer in the study of solar and stellar magnetic fields and for his ability to produce innovative instruments that enabled him to break new ground in astronomical research. His scientific career was no less important for his tenure as director of one of the leading astronomical centers of the world as he saw it through a period of tremendous expansion.

Origins. Babcock was born in Pasadena, California, to the astronomer Harold Delos Babcock and Mary Eliza Babcock. Harold Babcock had joined the staff of the Carnegie Institution of Washington’s new Mount Wilson Observatory three years earlier in 1909, coming from the National Bureau of Standards in Washington, DC. Harold Babcock became a renowned solar astronomer at the Mount Wilson Observatory and remained on the staff there until his retirement in 1948. During his early years Horace Babcock came to know the Mount Wilson Observatory and its staff quite well and naturally became interested in astronomy. With his father, the young Babcock visited the mountain observatory several times as a youth and he always remembered the noise and activity surrounding the

construction of the great 2.5-meter (8.2-foot) Hooker Telescope. In 1928 Babcock apprenticed in the observatory’s optical shop in Pasadena and learned the craft of instrument design and production. He entered the California Institute of Technology (Caltech) in 1930 and during his time there he assisted his father with his solar observations using the 45.72-meter (150-foot) solar tower telescope on Mount Wilson. After graduating with a BS in physics in 1934, Babcock decided to pursue his astronomical interests as a graduate student at the University of California at Berkeley.

Early Career. Babcock received his PhD in 1938 with the dissertation “On the Rotation of the Andromeda Nebula.” In his research Babcock, using the 0.9-meter (36-inch) Crossley reflecting telescope at Berkeley’s Lick Observatory on Mount Hamilton, California, measured the rotation of the nebula, now known as the Andromeda Galaxy (or M31), at various distances from its center in order to determine the distribution of mass throughout the galaxy. An interesting result of his research was the realization that the mass-to-luminosity ratio of M31 actually increases as one moves away from the bright central region of the galaxy. In the early 2000s some astronomers pointed to Babcock’s research as the first observational evidence of dark matter, though it was overlooked by many at first.

Babcock remained at the Lick Observatory for one more year after his graduation as a research assistant. In 1939 he presented a paper on his M31 research at a conference marking the dedication of the 2.1-meter (84-inch) telescope of the new McDonald Observatory in Texas. Primarily on the basis of his presentation, Babcock was hired immediately as an instructor and staff member of the McDonald Observatory by the University of Chicago (which operated the observatory for the University of Texas). Having learned the shortcomings of doing galactic spectroscopy with the Mayall nebular spectrograph at the Lick Observatory, Babcock designed a much faster spectrograph for galactic spectrum analysis at the McDonald telescope; the instrument proved to be a great success for many astronomers in the coming years.

When the United States entered World War II, the University of Chicago allowed Babcock to do war work on radar development at the Radiation Laboratory of the Massachusetts Institute of Technology. In 1942 he transferred back home, joining the rocket project at Caltech.

Research at the Mount Wilson Observatory. With the end of the war, Babcock planned to return to his normal duties for the University of Chicago but before he left Caltech he was offered a job on the staff of the Mount Wilson Observatory by its new incoming director, Ira S. Bowen, who had also been with the Caltech rocket project during the war. At Mount Wilson (which would soon become the Mount Wilson and Palomar Observatories in 1948), Babcock split his duties between research in solar and stellar magnetism and the development of new astronomical instruments. His first significant instrument design was a microdensitometer that was to be used to study the spectrographs produced by both the 2.5-meter(8.2-foot) Hooker Telescope and the soon-to-be-completed 5-meter (16.4-foot) Hale Telescope on Mount Palomar. The device produced excellent results but proved difficult to work with except by the most resolute observers and Babcock thus considered it a failure.

His researches in solar magnetism were initially carried out in collaboration with his father Harold, who still worked at the Mount Wilson Observatory. Even after the latter retired in 1948, they continued their joint investigations at the observatory’s Hale Solar Laboratory in Pasadena. Astronomers had measured strong magnetic fields in sunspots early in the twentieth century (up to a few thousand gauss). In the Babcocks’ work, Horace invented and developed the first solar magnetograph, which enabled the pair to detect weak magnetic fields on the sun’s surface. Using an early version of the magneto-graph, by the mid-1950s the Babcocks showed that the general magnetic field of the sun was about one gauss, much weaker than the spurious results reported by George Ellery Hale earlier in the century. In 1961 Horace Babcock proposed a magnetohydrodynamic model to explain sunspots and their magnetism through the differential rotation of the Sun (where the equatorial region of the Sun rotates faster than the poles).

Babcock extended his magnetic work to the distant stars as well as the Sun. While the Sun’s magnetic field is too weak to be detected at stellar distances, it was believed that some stars might have stronger fields that could be detected. Babcock’s work was quickly rewarded as he discovered the first example of a stellar magnetic field on the star 78 Virginis in 1946. By studying the Zeeman effect— that is, the splitting of a spectral line into a number of components due to the presence of a magnetic field—in the lines of that star’s spectrum, he found a general magnetic field of 1,500 gauss at the pole. Babcock subsequently discovered over 150 stars with measurable magnetic fields and this led to the publication in 1958 of his important article “A Catalog of Magnetic Stars.”

Babcock’s gift for designing instruments led him to the development and refinement, with his father at first, of the ruling engines at the Mount Wilson Observatory for the production of reflection diffraction gratings. Babcock implemented a number of design improvements, including using interferometric control of the diamond that would rule the lines in the gratings. His greatest achievement here was probably his production of the four optically matched gratings that would be used for the 5-meter (200-inch) Hale Telescope’s spectrograph. The gratings produced by Babcock and his technicians in the 1950s were the best available and many were liberally loaned to observatories all over the world. It would not be overstating the case to say that the Mount Wilson and Palomar Observatories, through its use and loan of diffraction gratings, was involved in most of the astronomical spectroscopy being carried out in the 1940s and 1950s.

Babcock also designed monitors to test atmospheric seeing conditions; these were used by the Mount Wilson and Palomar staff and other observatories to determine the best locations for new telescopes. As he pursued this line of work, he proposed in 1953 a new method of compensating for atmospheric effects in optical observations.

His research led to the development of what was later called adaptive optics, a technology that allows telescopes to quickly modify their optical components to cancel out the effects of turbulence in the atmosphere.

Observatory Director. On 1 July 1964, Babcock became the director of the Mount Wilson and Palomar Observatories (soon to be renamed the Hale Observatories). His administrative abilities had come to the fore when he had been appointed assistant director in 1957. Eventually, with his scientific, technical, and administrative experience, he became the logical successor to Bowen as director when the latter retired in 1964. Although Babcock’s interests lay far removed from administrative duties, he saw the directorship as an opportunity to seriously pursue his desire to establish a large telescope in the Southern Hemisphere. As director, Bowen had been able to successfully complete the Hale Telescope, get it into operational condition, and integrate it nicely into the astronomical research milieu, so the time was right for Babcock to take the next step in the observatory’s development.

Thanks to Babcock’s urgings to start planning for a southern telescope soon after he became assistant director, preparations in the form of site surveys for the new Southern Observatory of the Carnegie Institution of Washington, or CARSO, had already begun when he became director. The initial plan was to have a 5-meter (16.4-foot) telescope as the new observatory’s centerpiece with smaller supporting instruments, including a 1.2-meter (48-inch) Schmidt camera. Babcock oversaw a complex operation, which involved site testing in Australia, South Africa, and Chile, followed by intricate efforts to obtain the land for CARSO in Chile. Babcock was the chief negotiator with the Chilean president Eduardo Frei Montalva, in the successful bid to obtain a parcel of land on the ridge of the Las Campanas peaks at an altitude of 2,400 meters (7,874 feet) on the western range of the Andes. In order to gain help with funding for construction and operation, the Carnegie Institution had discussions with Canada, Great Britain, and Australia in order to see if these countries were interested in a joint southern venture. These plans did not reach fruition, and CARSO had to be diminished in scope from its original concept. The program was rewarded with the official opening of what became the Las Campanas Observatory in 1972, first with the 1-meter (40-inch) Henrietta Swope Telescope and later with the Irénée du Pont Telescope, a 2.5-meter (100-inch) instrument (reduced in size from the planned 5-meter telescope) that became operational in 1977.

Other administrative issues during Babcock’s tenure as director included: the unsuccessful attempt to move the Mount Wilson and Palomar Observatories headquarters onto a site on the Caltech campus; the start of the observatories’ pursuing federal funds, including the attempt to obtain general operating support from the National Science Foundation, and the competition for these funds from Kitt Peak National Observatory; the construction and dedication in 1970 of the 1.5-meter (4.9-foot) telescope on Palomar Mountain to take some of the lighter duties away from the 5-meter (16.4-foot) telescope; Babcock’s personal involvement in the failed efforts to build a science museum in Pasadena; Babcock’s involvement in the National Academy of Science’s efforts to define the future needs of American astronomy, in talks with Harvard about constructing a Shapley Memorial Telescope at Las Campanas, and in discussions with the Massachusetts Institute of Technology on their becoming a part of the Hale Observatories (which they did not).

Retirement. Babcock retired from the Hale Observatories in 1978, having successfully established the observatories in the Southern Hemisphere. He continued to work at the observatories’ headquarters in Pasadena for another twenty years on various projects mostly related to adaptive optics and telescope mountings. In 1998 he moved to a retirement community in Santa Barbara, California, where he continued to concentrate on astronomical instrumentation until a few months before his death in 2003.

Babcock’s awards from his peers include the Draper Medal of the National Academy of Sciences (1957), the Eddington Medal (1958) and the Gold Medal (1970) of the Royal Astronomical Society, and the Bruce Gold Medal of the Astronomical Society of the Pacific (1969). Because of Babcock’s natural reticence, little is known of his private life except that he did have two children from a first wife and one child from his second wife, Elizabeth

M. Jackson. Both marriages ended in divorce. One of his true enjoyments was sailing, and for several years he owned a sailboat that he could retreat to along with an occasional colleague. The boat was equipped with a number of homemade electronic gadgets made by Babcock, including one that enabled the ship to steer itself by sensing the Earth’s magnetic field relative to the course he set.


An important archival resource is Babcock’s collection of papers as director of the Mount Wilson and Palomar Observatories (later Hale Observatories). These are on permanent deposit at the Henry E. Huntington Library in San Marino, California, as part of the archives of the Observatories of the Carnegie Institution of Washington. There is an oral history interview with Babcock available at the AIP’s Center for the History of Physics.


“On the Rotation of the Andromeda Nebula.” PhD diss., University of California, Berkeley, 1938. A work that continued into the early 2000s to be cited in reviews about “dark matter.” “Zeeman Effect in Stellar Spectra.” Astrophysical Journal 105 (1947): 105–119. The initial discovery of large magnetic fields in stars.

“The Possibility of Compensating Astronomical Seeing.” Publications of the Astronomical Society of the Pacific 65 (1953): 229–236. A paper that is generally regarded as being the first to discuss adaptive optics.

“A Catalog of Magnetic Stars.” Astrophysical Journal SupplementSeries 3 (1958): 141–210. The culmination of Babcock’s research on magnetic stars.

“The Topology of the Sun’s Magnetic Field and the 22-Year Cycle.” Astrophysical Journal. 133 (1961): 572–587. The model proposed here continues to be the basis of current models of solar magnetism.

“Diffraction Gratings at the Mount Wilson Observatory.” Vistas in Astronomy 29 (1986): 153–174. A helpful memoir that includes details about the Babcocks’ work with diffraction gratings.

With T. G. Cowling. “General Magnetic Fields in the Sun and Stars (Report on Progress of Astronomy).” Monthly Notices of the Royal Astronomical Society 113 (1953): 357–381. A magisterial summary of the state of the new field of magnetohydrodynamics.


Abell, George Osgood. “Award of the Bruce Gold Medal to Dr.Horace W. Babcock.” Publications of the Astronomical Society of the Pacific 81 (1969): 179–183.

Lovell, Sir Bernard. “Award of Gold Medal to Dr. Horace Welcome Babcock (address).” Quarterly Journal of the Royal Astronomical Society11 (1970): 85–87.

Preston, George W. “Horace Welcome Babcock (1912–2003).” Publications of the Astronomical Society of the Pacific 116 (2004): 290–294.

Sandage, Allan. “Horace Welcome Babcock.” Proceedings of theAmerican Philosophical Society 150 (2006): 152–160. Some of the dates mentioned in this paper do not match those reflected in Babcock’s own papers.

Vaughan, Arthur H. “Horace Welcome Babcock, 1912–2003.” Bulletin of the American Astronomical Society 35 (2003): 1454–1455.

Ronald Brashear

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